The present invention relates to the general field of turbomachines provided with devices for automatically detecting ferromagnetic particles in an oil enclosure.
The invention relates more particularly to an aeroengine in which the electricity generator is formed by a secondary magnetic circuit secured to one of its stators and a primary magnetic circuit constrained to rotate with one of its rotors.
In the field of aeroengines, ancillaries (e.g. actuators) are generally mostly hydraulic. For reasons of reliability, safety, and compactness, it is becoming more and more common for such hydraulic ancillaries to be replaced by electrical ancillaries.
For this purpose, it has become necessary to include an electricity generator in a turbomachine having electrical ancillaries. Such a generator serves simultaneously to feed electricity to the various items of electrical equipment belonging to the turbomachine (pumps, actuators, etc.), and also to start the turbomachine.
In order to take advantage of the arms (or spacers) that hold the turbomachine casing, for the purpose of passing electric cables, the solution that is generally selected is to install such an electricity generator in one of the oil enclosures of the high pressure body of the turbomachine. Such an oil enclosure is used to cool and lubricate the ball bearings between the various shafts. Typically, the electricity generator comprises a coil (forming a secondary magnetic circuit) and magnets (forming a primary magnetic circuit) that are secured respectively to the stator and to the rotor of the high-pressure turbine of the turbomachine.
In addition, it is also known to fit the oil enclosures of turbomachines with detectors for detecting wear of the ball bearings between the shafts and associated with said enclosures. Such sensors are generally in the form of external magnetic plugs. These plugs comprise magnets that capture the ferromagnetic particles inside the oil enclosure that stem from ball bearing wear. During ground maintenance operations on the turbomachine, the magnetic plugs are dismantled from the turbomachine and spectrographic analysis is used to determine the origins and the quantities of the particles that have been collected in order to deduce therefrom the wear state of the ball bearings.
When the turbomachine is fitted with an electricity generator as described above, the problem arises of how to detect ball bearing wear. The presence of magnets constituting the primary magnetic circuit of the electricity generator inside the oil enclosure has the consequence of falsifying bearing wear detection by means of magnetic plugs.
More generally, detecting ball bearing wear by means of magnetic plugs turns out to be an operation that is time consuming and incomplete. In addition to the fact that spectrographic analysis is necessary, the magnetic plugs can be read only on specific occasions (only while the turbomachine is being subjected to maintenance on the ground). As a result the level of ball bearing wear is sometimes detected only late, and that can compromise turbomachine safety.